1. Field of the Invention
The invention relates generally to the synchronization of data and more particularly to the synchronization of sampled audio data between multiple channels of an audio amplification system.
2. Related Art
Pulse Width Modulation (PWM) or Class D signal amplification technology has existed for a number of years. PWM technology has become more popular with the proliferation of Switched Mode Power Supplies (SMPS). Since this technology emerged, there has been an increased interest in applying PWM techniques in signal amplification applications as a result of the significant efficiency improvement that can be realized through the use of Class D power output topology instead of the legacy (linear Class AB) power output topology.
While PWM techniques have advanced and become more widely applicable to various types of systems, they still suffer from a variety of problems. For example, the performance and quality characteristics of Class D amplifiers typically vary with the particular applications in which they are used. The exact implementation of the total system solution and the end-user application is not deterministic, and hence cannot be accounted for apriori. With the existing technologies, designs require point solutions that are not flexible, scalable or transportable across applications.
Further, Class D amplifiers are extremely sensitive to unstable or variable clock domains. The quality and performance of these systems may therefore be much lower than desired when they are used in situations where the integrity, frequency and stability of the digital input signal is unknown. Even in situations where these factors are well-known and were controlled, the clock domain of the amplifier itself must be extremely stable.
As a result of these problems, Class D amplifiers are not easily adaptable to the requirements of many mainstream systems. Consider, for example, a multi-channel audio applications such as a home theater system. Typically, such a system has too many channels to be handled by a single integrated Class D unit, which might have two channels, each capable of handling a stereo pair of signals. It would therefore be necessary to use multiple units. Running multiple units side-by-side requires synchronization and output data phase alignment which is generally beyond the capabilities of most Class D systems. Resulting errors may cause phase mismatches which are audible and which may noticeably degrade the quality of the sound produced by the system.
One prior art system attempts to address the synchronization of multiple channels by sharing sample rate ratio information. In this system, multiple channels process audio data streams. Each of these channels converts data from a received sample rate to a desired output sample rate. The ratio of the output rate to the input rate is computed for one channel and then passed to the other channels. This solution, however, requires quite a bit of overhead in the computation of the ratio and the transmission of the resulting information to the other channels. Further, it does not account for the variations in sample rates from one channel to another.